Polymeric acrylic acid derivatives are usually prepared commercially by free-radical polymerization initiated by initiators which form free radicals and the chain is terminated when two of the free radicals formed react with one another. In this process, polymers having a high molecular weight but a very broad molecular weight distribution can be obtained.
Anionic polymerization of acrylic acid derivatives is also known which is not initiated by free radicals but instead by initiators which form anions, such as organoalkali metal compounds. This type of polymerization forms so-called "living polymers" which have active terminal groups since chain termination by reaction of two ions of the same charge is not possible. The chain termination can be affected artificially, for example, by adding water or alcohol. This process has certain disadvantages since the narrow molecular weight distribution which is desired can only be achieved at low temperatures, for example, up to -80.degree.C., and using very pure starting materials (cf. U.S. Pat. No. 4,351,924 to Andrews et al).
The polymerization of acrylic acid derivatives which has become known under the term "quasi-ionic" polymerization has a similar basis. In this process, the initial reaction is initiated by certain selected initiators together with nucleophilic or electrophilic catalysts to form living polymers. Selected initiators are known compounds of silicon, germanium and tin in which the elements mentioned are bonded to oxygen or carbon atoms, such as trimethylsilylketene acetals or trimethylsilyl cyanide (cf. U.S. Pat. No. 4,414,372 to Farnham et al; U.S. Pat. No. 4,417,034 to Webster; U.S. Pat. No. 4,508,880 to Webster; U.S. Pat. No. 4,524,196 to Farnham et al; U.S. Pat. No. 5 4,588,795 to Dicker et al; and U.S. Pat. No. 4,732,955 to Dicker). This process can be carried out at room temperature and above, but again requires starting materials of high purity, and in addition, only forms polymers having a narrow molecular weight distribution if methacrylic acid derivatives are used.
Initiators of the mercaptosilane type give living polymers having a narrow molecular weight distribution under the quasi-ionic polymerization conditions, even when acrylic acid derivatives are used as monomers (cf. U.S. Pat. No. 4,626,579 to Reetz et al).
According to the prior art, polymers having a narrow molecular weight distribution, but with mean molecular weights themselves which are generally relatively low, are obtained from monomeric acrylic acid derivatives of any type with the aid of quasi-ionic polymerization using certain organosilicon compounds as initiators in combination with nucleophilic or electrophilic catalysts.
Therefore, it is an object of the present invention to provide an improved process for the polymerization of polar compounds which have a C.dbd.C double bond in the .alpha.-position to a carbonyl, nitrile, nitro, sulfone or phosphone group. Another object of the present invention is to provide an improved process for the polymerization of polar compounds having a C.dbd.C double bond in which the polymerization is initiated by organometallic compounds as initiators together with nucleophilic or electrophilic catalysts at a temperature of from about -100.degree.C. to +100.degree.C. A further object of the present invention is to provide an improved process for the polymerization of polar compounds other than acrylic acid derivatives which yields polymers having both a high mean molecular weight and also a narrow molecular weight distribution.